This is a proposal to expand a family study of adjudicated adolescent boys and girls with Substance Use Disorders (SUD) and Conduct Disorder (CD). In this revised application, we propose to evaluate the families of 400 adolescent probands, identified through court records, as well as 200 controls and their family members. Expanding the study to include more families will allow for an adequate sample size to discriminate between different comorbidity models of SUD and CD and the assessment of parental and sibling influences on SUD and CD. DNA will be collected in order to assess for degree of genetic relatedness and non-paternity. The specific aims of the proposal are to: 1) test competing models of the comorbidity between SUD and CD in sibling pairs, where one of the siblings is an adjudicated adolescent, 2) examine the influence of parents and siblings on the development of SUD and CD in families with at least one adjudicated adolescent, and 3) compare the observed familial aggregation of SUD and CD between the proposed sample and a sample of families of youth in treatment for SUD and CD. SUD and CD are severe, life-threatening conditions of adolescence. Mortality rates among such adolescents reportedly are fivefold greater than among their age-mates. This research may lead to the identification of familial influences influencing the expression of these pathological behaviors. This may lead to improved phenotypes, improving the search for specific genetic or environmental causes of these destructive behaviors. The ultimate goal of this research is to reverse that process through therapeutic correction of those pathological genetic or environmental factors.